The Principal Investigator has been pursuing research work pertaining to the virus-cell, virus-host and cell-host interactions, in the SV40-hamster cell system, both in vitro and in vivo. In studies of the virus-cell interaction, he has attempted to define the relative role of the viral genome virus, that of the cell genome in determining tumor-cell morphogenesis and tumor-cell differentiation, and the significance of the various virus-mediated cellular neoantigens relative to each other, to the integrated viral genome, and to the expression of a morphological and physiological state of transformation. In relation to the virus-host interaction, he has endeavored to assess the virus-dependent (dose, route of inoculation) and host-dependent (age) factors that influence the incidence, latency and morphological variability of tumors induced by the oncogenic virus, and the significance of the development of antibody to the viral and virus-related cellular antigens in the establishment of a neoplasm in the intact host. In regard to the cell-host interaction, he has tried to define the parameters that are responsible: for initiation of the oncogenic state, for variability of severity in oncogenic potential at the cellular level, for progression from a less to a more aggressive behavior and for the response of the host to the presence of the tumor.